The structure and activity of tRNA are under investigation in several projects. The mechanism, breadth of occurrence, and in vivo role of the hydrolytic correction mechanism for aminoacyl-tRNA's are being sought by genetic and biochemical means. The biochemistry of the Su7 plus amber suppressor is being pursued, with an eye to explaining its conversion by a mutated anticodon, from a tRNAtry to a tRNAgln. The relation between the usual preparations of tRNA and its in vivo state is being investigated by fast isolation techniques. The solution conformation of tRNA is being sought by a specific cross-linking and sequencing technique being developed in this laboratory.